Vehicle engine systems may comprise one or more aspirators coupled to an intake air passage of an engine to harness engine airflow for generation of vacuum for use by various vacuum-actuated devices such as a brake booster. Aspirators (which may alternatively be referred to as ejectors, venturi pumps, jet pumps, and eductors) are passive devices that can provide low-cost vacuum generation, wherein an amount of vacuum generated at an aspirator can be controlled with a flow regulating valve controlling the motive air flow rate through the aspirator. For example, when incorporated in an engine intake system, aspirators may generate vacuum using energy that would otherwise be lost to throttling, and the generated vacuum may be used in vacuum-powered devices such as brake boosters.
Cunningham (U.S. Patent Application 2012/0285421) discloses a method for controlling engine vacuum production wherein when an engine is running, fuel is being supplied to the engine, and a vacuum level of a vacuum actuated device is below a threshold level, vacuum is supplied to the vacuum actuated device via the engine intake manifold while the engine throttle is closed and an ejector valve is closed. Furthermore, when a vacuum level of a vacuum actuated device is above a threshold level, vacuum is supplied to the vacuum actuated device via the engine intake manifold and via an ejector by directing engine intake air through the ejector.
The inventors herein have recognized potential issues with the above conventional approaches. Namely, closing the throttle when supplying vacuum to vacuum actuated devices when a vacuum level of a vacuum actuated device is below a threshold level may be detrimental to fuel economy, engine emissions, NVH, vehicle drivability, vehicle operability, and the like. Furthermore, during idling in a hybrid-electric vehicle system, the engine is decoupled from the propulsion system, and thus conventional methods may not address supplying vacuum to vacuum actuated devices when fuel is not being supplied to the engine. Further still, a hybrid-electric vehicle may remain stationary even when the brake pedal is not fully depressed. Accordingly, operators of hybrid-electric vehicles may bobble the brake pedal while idling, which can deplete the brake booster vacuum. Owing to the engine being off during idling, the brake booster vacuum is conventionally restored by automatically performing an engine pull-up so that intake manifold vacuum may be supplied to the vacuum actuated device. In this way, bobbling the brake actuator may be detrimental to overall fuel economy.
One approach that at least partially addresses the aforementioned issues is a method for a hybrid-electric vehicle, comprising while the hybrid-electric vehicle is moving and in an absence of fuel being directed to an engine, directing engine intake air through an ejector to supply vacuum to a brake booster independent of a brake booster vacuum.
In another embodiment, a method for a hybrid vehicle may comprise during a second condition, comprising when an engine intake manifold vacuum is greater than a threshold intake manifold vacuum, directing engine intake air through an ejector to draw vacuum from a brake booster independent of a brake booster vacuum. Furthermore, during a first condition, the method may comprise while the hybrid-electric vehicle is moving and in an absence of fuel being directed to the engine, directing engine intake air through the ejector to supply vacuum to the brake booster independent of the brake booster vacuum.
In another embodiment, a method for a hybrid vehicle system may comprise, independent of a vacuum level of a vacuum reservoir, during a condition when the hybrid vehicle system is propelled only with motor torque, opening a valve fluidly coupled to an ejector, whereupon opening the valve, vacuum is drawn from the ejector to the vacuum reservoir.
By supplying vacuum to a brake booster independent of brake booster vacuum, for example, even when a brake booster vacuum is greater than a threshold brake booster vacuum and not only when a brake booster vacuum is less than a threshold brake booster vacuum, a length of time during which the brake booster vacuum is greater than a threshold brake booster vacuum level is increased. In this way, the above embodiments achieve at least the technical result of reducing the frequency of engine pull-ups, thereby improving overall fuel economy as compared to conventional methods and systems.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.